76 research outputs found
Using Narrow Band Photometry to Classify Stars and Brown Dwarfs
We present a new system of narrow band filters in the near infrared that can
be used to classify stars and brown dwarfs. This set of four filters, spanning
the H band, can be used to identify molecular features unique to brown dwarfs,
such as H2O and CH4. The four filters are centered at 1.495 um (H2O), 1.595 um
(continuum), 1.66 um (CH4), and 1.75 um (H2O). Using two H2O filters allows us
to solve for individual objects' reddenings. This can be accomplished by
constructing a color-color-color cube and rotating it until the reddening
vector disappears. We created a model of predicted color-color-color values for
different spectral types by integrating filter bandpass data with spectra of
known stars and brown dwarfs. We validated this model by making photometric
measurements of seven known L and T dwarfs, ranging from L1 - T7.5. The
photometric measurements agree with the model to within +/-0.1 mag, allowing us
to create spectral indices for different spectral types. We can classify A
through early M stars to within +/-2 spectral types, late-type M and L dwarfs
to within +/-0.3 spectral types and T dwarfs to within +/-0.1 spectral types
1-sigma. Thus, we can distinguish between a T1 and a T3 dwarf. The four
physical bands can be converted into two reddening-free indices, mu1 and mu2,
and an extinction, AV, for the individual object. This technique, which is
equivalent to extremely low resolution spectroscopy, can be used to survey
large areas to provide rough spectral classifications for all the stars in the
area, ranging down to the coolest brown dwarfs. It should prove particularly
useful in young clusters where reddening can be high.Comment: 20 pages, 8 figures, submitted 18 Aug. 2003, accepted 5 Dec. 2003 to
Ap
Simulating the detection of the global 21 cm signal with MIST for different models of the soil and beam directivity
The Mapper of the IGM Spin Temperature (MIST) is a new ground-based,
single-antenna, radio experiment attempting to detect the global 21 cm signal
from the Dark Ages and Cosmic Dawn. A significant challenge in this measurement
is the frequency-dependence, or chromaticity, of the antenna beam directivity.
MIST observes with the antenna above the soil and without a metal ground plane,
and the beam directivity is sensitive to the electrical characteristics of the
soil. In this paper, we use simulated observations with MIST to study how the
detection of the global 21 cm signal from Cosmic Dawn is affected by the soil
and the MIST beam directivity. We simulate observations using electromagnetic
models of the directivity computed for single- and two-layer models of the
soil. We test the recovery of the Cosmic Dawn signal with and without beam
chromaticity correction applied to the simulated data. We find that our
single-layer soil models enable a straightforward recovery of the signal even
without chromaticity correction. Two-layer models increase the beam
chromaticity and make the recovery more challenging. However, for the model in
which the bottom soil layer has a lower electrical conductivity than the top
layer, the signal can be recovered even without chromaticity correction. For
the other two-layer models, chromaticity correction is necessary for the
recovery of the signal and the accuracy requirements for the soil parameters
vary between models. These results will be used as a guideline to select
observation sites that are favorable for the detection of the Cosmic Dawn
signal.Comment: Accepted for publication in the Astrophysical Journa
MeerKLASS: MeerKAT Large Area Synoptic Survey
We discuss the ground-breaking science that will be possible with a wide area
survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area
Synoptic Survey). The current specifications of MeerKAT make it a great fit for
science applications that require large survey speeds but not necessarily high
angular resolutions. In particular, for cosmology, a large survey over for hours will potentially provide the first
ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of
dark energy. The combination with multi-wavelength data will give unique
additional information, such as exquisite constraints on primordial
non-Gaussianity using the multi-tracer technique, as well as a better handle on
foregrounds and systematics. Such a wide survey with MeerKAT is also a great
match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era
for galaxies resolved in the HI emission line beyond local structures at z >
0.01. It will also produce a large continuum galaxy sample down to a depth of
about 5\,Jy in L-band, which is quite unique over such large areas and
will allow studies of the large-scale structure of the Universe out to high
redshifts, complementing the galaxy HI survey to form a transformational
multi-wavelength approach to study galaxy dynamics and evolution. Finally, the
same survey will supply unique information for a range of other science
applications, including a large statistical investigation of galaxy clusters as
well as produce a rotation measure map across a huge swathe of the sky. The
MeerKLASS survey will be a crucial step on the road to using SKA1-MID for
cosmological applications and other commensal surveys, as described in the top
priority SKA key science projects (abridged).Comment: Larger version of the paper submitted to the Proceedings of Science,
"MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 201
GBT/MUSTANG-2 9" resolution imaging of the SZ effect in MS0735.6+7421: Confirmation of the SZ Cavities through direct imaging
Mechanical feedback from active galactic nuclei (AGN) is thought to be the
dominant feedback mechanism quenching cooling flows and star formation in
galaxy cluster cores. However, the mechanisms by which AGN couple to the
intracluster medium (ICM) are not well understood. The nature of pressure
supporting the cavities is not known. Using the MUSTANG-2 instrument on the
Green Bank Telescope (GBT), we aimed to measure thermal Sunyaev-Zeldovich (SZ)
effect signals associated with the X-ray cavities in MS0735.6+7421, a moderate
mass cluster hosting one of the most energetic AGN outbursts known. We use
these measurements to infer the level of non-thermal sources of pressure, such
as magnetic fields and turbulence, as well as relativistic and cosmic ray
components, supporting the cavities. We used preconditioned gradient descent to
fit a model for the cluster, cavities, and central point source directly to the
time ordered data of the MUSTANG-2 signal. We use this model to probe the
thermodynamic state of the cavities. We have shown that the SZ signal
associated with the cavities is suppressed compared to the expectations for a
thermal plasma with the temperature few tens keV. The smallest value of
the suppression factor that is consistent with the data is 0.4, lower
than inferred in earlier work. Larger values of are possible once the
contribution of the cocoon shock surrounding the bubbles is taken into account.
The baseline model with this particular geometrical setup yields best-fitting
value f~0.5, which at face value implies a mix of thermal and non-thermal
pressure support. Larger values of (up to 1, i.e. no tSZ signal from the
bubbles) are still possible when allowing for variations in the line-of-sight
geometry.Comment: 8 pages, 3 figure
Observing the Evolution of the Universe
How did the universe evolve? The fine angular scale (l>1000) temperature and
polarization anisotropies in the CMB are a Rosetta stone for understanding the
evolution of the universe. Through detailed measurements one may address
everything from the physics of the birth of the universe to the history of star
formation and the process by which galaxies formed. One may in addition track
the evolution of the dark energy and discover the net neutrino mass.
We are at the dawn of a new era in which hundreds of square degrees of sky
can be mapped with arcminute resolution and sensitivities measured in
microKelvin. Acquiring these data requires the use of special purpose
telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and
the South Pole Telescope (SPT). These new telescopes are outfitted with a new
generation of custom mm-wave kilo-pixel arrays. Additional instruments are in
the planning stages.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 177 author available at http://cmbpol.uchicago.ed
A two-component protease in Methylorubrum extorquens with high activity toward the peptide precursor of the redox cofactor pyrroloquinoline quinone
Pyrroloquinoline quinone is a prominent redox cofactor in many prokaryotes, produced from a ribosomally synthesized and post-translationally modified peptide PqqA via a pathway comprising four conserved proteins PqqB?E. These four proteins are now fairly well-characterized and span radical SAM activity (PqqE), aided by a peptide chaperone (PqqD), a dual hydroxylase (PqqB), and an eight-electron, eight-proton oxidase (PqqC). A full description of this pathway has been hampered by a lack of information regarding a protease/peptidase required for the excision of an early, cross-linked di-amino acid precursor to pyrroloquinoline quinone. Herein, we isolated and characterized a two-component heterodimer protein from the ?-proteobacterium Methylobacterium (Methylorubrum) extorquens that can rapidly catalyze cleavage of PqqA into smaller peptides. Using pulldown assays, surface plasmon resonance, and isothermal calorimetry, we demonstrated the formation of a complex PqqF/PqqG, with a K-D of 300 nm. We created a molecular model of the heterodimer by comparison with the Sphingomonas sp. A1 M16B Sph2681/Sph2682 protease. Analysis of time-dependent patterns for the appearance of proteolysis products indicates high specificity of PqqF/PqqG for serine side chains. We hypothesize that PqqF/PqqG initially cleaves between the PqqE/PqqD-generated cross-linked form of PqqA, with nonspecific cellular proteases completing the release of a suitable substrate for the downstream enzyme PqqB. The finding of a protease that specifically targets serine side chains is rare, and we propose that this activity may be useful in proteomic analyses of the large family of proteins that have undergone post-translational phosphorylation at serine.National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [GM118117, GM124002, 1S10OD020062-01
Residual ground-water levels of the neonicotinoid thiacloprid perturb chemosensing of Caenorhabditis elegans
© 2017, The Author(s). This study investigated the neurological effects of residual ground-water levels of thiaclopridon the non-target organism Caenorhabditis elegans. Nematodes treated with thiacloprid showed a dose-dependent and significantly increased twitch response at concentrations above 50 ng mL−1 that disabled their forward locomotion in liquid culture. In comparison with untreated controls, 10 ng mL−1 thiacloprid perturbed the chemosensory ability of C. elegans such that the nematodes no longer demonstrated positive chemotaxis towards a NaCl chemo-attractant, reducing their chemotaxis index from +0.48 to near to zero. Nematodes also exhibited a locomotion characteristic of those devoid of chemo-attraction, making significantly more pirouetting turns of ≥90° than the untreated controls. Compared to the untreated controls, expression of the endocytosis-associated gene, Rab-10, was also increased in C. elegans that had developed to adulthood in the presence of 10 ng mL−1 thiacloprid, suggesting their active engagement in increased recycling of affected cellular components, such as their nAChRs. Thus, even residual, low levels of this less potent neonicotinoid that may be found in field ground-water had measurable effects on a beneficial soil organism which may have environmental and ecological implications that are currently poorly understood
The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and its Implications for Structure Growth
We present new measurements of cosmic microwave background (CMB) lensing over
sq. deg. of the sky. These lensing measurements are derived from the
Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB dataset, which
consists of five seasons of ACT CMB temperature and polarization observations.
We determine the amplitude of the CMB lensing power spectrum at
precision ( significance) using a novel pipeline that minimizes
sensitivity to foregrounds and to noise properties. To ensure our results are
robust, we analyze an extensive set of null tests, consistency tests, and
systematic error estimates and employ a blinded analysis framework. The
baseline spectrum is well fit by a lensing amplitude of
relative to the Planck 2018 CMB power spectra
best-fit CDM model and relative to
the best-fit model. From our lensing power
spectrum measurement, we derive constraints on the parameter combination
of
from ACT DR6 CMB lensing alone and
when combining ACT DR6 and Planck NPIPE
CMB lensing power spectra. These results are in excellent agreement with
CDM model constraints from Planck or
CMB power spectrum measurements. Our lensing measurements from redshifts
-- are thus fully consistent with CDM structure growth
predictions based on CMB anisotropies probing primarily . We find no
evidence for a suppression of the amplitude of cosmic structure at low
redshiftsComment: 45+21 pages, 50 figures. Prepared for submission to ApJ. Also see
companion papers Madhavacheril et al and MacCrann et a
The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters
We present cosmological constraints from a gravitational lensing mass map
covering 9400 sq. deg. reconstructed from CMB measurements made by the Atacama
Cosmology Telescope (ACT) from 2017 to 2021. In combination with BAO
measurements (from SDSS and 6dF), we obtain the amplitude of matter
fluctuations at 1.8% precision,
and the Hubble
constant at
1.6% precision. A joint constraint with CMB lensing measured by the Planck
satellite yields even more precise values: ,
and . These measurements agree
well with CDM-model extrapolations from the CMB anisotropies measured
by Planck. To compare these constraints to those from the KiDS, DES, and HSC
galaxy surveys, we revisit those data sets with a uniform set of assumptions,
and find from all three surveys are lower than that from ACT+Planck
lensing by varying levels ranging from 1.7-2.1. These results motivate
further measurements and comparison, not just between the CMB anisotropies and
galaxy lensing, but also between CMB lensing probing on
mostly-linear scales and galaxy lensing at on smaller scales. We
combine our CMB lensing measurements with CMB anisotropies to constrain
extensions of CDM, limiting the sum of the neutrino masses to eV (95% c.l.), for example. Our results provide independent
confirmation that the universe is spatially flat, conforms with general
relativity, and is described remarkably well by the CDM model, while
paving a promising path for neutrino physics with gravitational lensing from
upcoming ground-based CMB surveys.Comment: 30 pages, 16 figures, prepared for submission to ApJ. Cosmological
likelihood data is here:
https://lambda.gsfc.nasa.gov/product/act/actadv_prod_table.html ; likelihood
software is here: https://github.com/ACTCollaboration/act_dr6_lenslike . Also
see companion papers Qu et al and MacCrann et al. Mass maps will be released
when papers are publishe
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